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Subject: [Bug 201611] [patch] Add devfs_get_cdevpriv_from_file(9)
Date: Tue, 29 Sep 2015 00:43:28 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=201611

--- Comment #8 from Andy Ritger <aritger@nvidia.com> ---
(In reply to John Baldwin from comment #7)

Thanks, John.  Those are all fair points.  Looking back at my notes, the reason
we originally implemented our API as having user-space, rather than
kernel-space, create the file descriptor was that doing it in user-space
minimized how much in-kernel API churn we would be exposed to (i.e., concern
over the API for allocating an fd within the kernel changing across kernel
versions).  To be fair, that's much more of a concern on Linux than on FreeBSD.

In any case, having the ioctl return an fd for the resource should be workable.

On the receiving side, I worry that we may still need the flexibility of an
ioctl implementation within the kernel looking up information from a file
descriptor.

Are you very familiar with the Linux dma-buf interface?  There is some
documentation on it here:
    https://www.kernel.org/doc/Documentation/dma-buf-sharing.txt
I expect those working on porting DRM from Linux to FreeBSD will eventually
need to implement drm-buf on FreeBSD, and some of these same fd translation
questions will come up, there.

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